 |
Electronic Components Datasheet Search |
|
|
Electronic Components Datasheet Search |
|
LT1936EMS8E Datasheet(PDF) 9 Page - Linear Technology |
|
||||||||||||||||||||||||||||||
LT1936EMS8E Datasheet(HTML) 9 Page - Linear Technology |
|
|
9 / 20 page  LT1936 9 1936fd inductance may result in discontinuous mode operation, which is okay but further reduces maximum load current. For details of maximum output current and discontinuous mode operation, see Linear Technology Application Note 44. Finally, for duty cycles greater than 50% (VOUT/VIN > 0.5), there is a minimum inductance required to avoid subharmonic oscillations. Choosing L greater than 1.6 (VOUT + VD) μH prevents subharmonic oscillations at all duty cycles. Catch Diode A 1A Schottky diode is recommended for the catch diode, D1. The diode must have a reverse voltage rating equal to or greater than the maximum input voltage. The ON Semiconductor MBRM140 is a good choice. It is rated for 1A DC at a case temperature of 110°C and 1.5A at a case temperature of 95°C. Diode Incorporated’s DFLS140L is rated for 1.1A average current; the DFLS240L is rated for 2A average current. The average diode current in an LT1936 application is approximately IOUT (1 – DC). Input Capacitor Bypass the input of the LT1936 circuit with a 4.7μF or higher value ceramic capacitor of X7R or X5R type. Y5V types have poor performance over temperature and ap- plied voltage, and should not be used. A 4.7μF ceramic is adequate to bypass the LT1936 and will easily handle the ripple current. However, if the input power source has high impedance, or there is significant inductance due to long wires or cables, additional bulk capacitance may be necessary. This can be provided with a low performance electrolytic capacitor. Step-down regulators draw current from the input sup- ply in pulses with very fast rise and fall times. The input capacitor is required to reduce the resulting voltage ripple at the LT1936 and to force this very high frequency switching current into a tight local loop, minimizing EMI. A 4.7μF capacitor is capable of this task, but only if it is placed close to the LT1936 and the catch diode; see the PCB Layout section. A second precaution regarding the ceramic input capacitor concerns the maximum input voltage rating of the LT1936. A ceramic input capacitor combined with trace or cable inductance forms a high quality (under damped) tank circuit. If the LT1936 circuit is plugged into a live supply, the input voltage can ring to twice its nominal value, possibly exceeding the LT1936’s voltage rating. This situation is easily avoided; see the Hot Plugging Safety section. For space sensitive applications, a 2.2μF ceramic capaci- tor can be used for local bypassing of the LT1936 input. However, the lower input capacitance will result in in- creased input current ripple and input voltage ripple, and may couple noise into other circuitry. Also, the increased voltage ripple will raise the minimum operating voltage of the LT1936 to ~3.7V. Output Capacitor The output capacitor has two essential functions. Along with the inductor, it filters the square wave generated by the LT1936 to produce the DC output. In this role it determines the output ripple, and low impedance at the switching frequency is important. The second function is to store energy in order to satisfy transient loads and stabilize the LT1936’s control loop. Ceramic capacitors have very low equivalent series re- sistance (ESR) and provide the best ripple performance. A good value is: C V OUT OUT = 150 where COUT is in μF. Use X5R or X7R types. This choice will provide low output ripple and good transient response. Transient performance can be improved with a high value capacitor if the compensation network is also adjusted to maintain the loop bandwidth. A lower value of output capacitor can be used, but transient performance will suffer. With an external compensation network, the loop gain can be lowered to compensate for the lower capacitor value. When using the internal compensa- tion network, the lowest value for stable operation is: C V OUT OUT > 66 APPLICATIONS INFORMATION |
Similar Part No. - LT1936EMS8E |
|
Similar Description - LT1936EMS8E |
|
|
|
Link URL |
| Privacy Policy |
| ALLDATASHEET.COM |
| Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Datasheet Upload | Contact us | Privacy Policy | Link Exchange | Manufacturer List All Rights Reserved©Alldatasheet.com |
| Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
|
Family Site : ic2ic.com |
icmetro.com |
English ▼
English
Chinese
German
Japanese
Russian
Korean
Spanish
French
Italian
Portuguese
Polish
Vietnamese
Indian
Mexican
British
New Zealand
